The sensitivity of the total 12-lead QRS amplitude was compared to certain standard electrocardiographic criteria for left ventricular (LV) hypertrophy in 57 necropsy patients with hypertrophic cardiomyopathy (HC). The total 12-lead QRS amplitude ranged from 66 to 339 mm (mean 179) (10 mm = 1 mV). Using 175 mm as the upper limit of normal, this technique yielded a sensitivity of 53% which was the highest sensitivity of any criteria tested. The Sokolow-Lyon index had a sensitivity of 39%; the Romhilt-Estes voltage criteria, 37%; the Romhilt-Estes point score system, 49%, and the criterion of RV6 > RV5, 39%. No correlation was found between total 12-lead QRS voltage and heart weight, LV free wall thickness, LV peak systolic and end-diastolic pressures or LV outflow tract peak systolic pressure gradient. The 10 patients (18%) with transmural LV scars had significantly lower total 12-lead QRS voltage than did the 48 patients (78%) without such scars (155 mm - vs. - 205 mm, p=0.02). Total 12-lead QRS amplitude >175 mm is a useful indicator of LV hypertrophy, and among patients with HC it is more sensitive than other more commonly employed criteria.